Embryonic neural crest cells are the source of many adult cell types including the neurons of the sympathetic parasympathetic, and most sensory ganglia of the peripheral nervous system. Experimental evidence indicates that at least some aspects of neural crest development are influenced by the embryonic environment. The overall objective of our research is to understand the control of the differentiation of neural crest cells into neurons. During development some neural crest-derived neurons acquire the capacity to metabolize selected peptide molecules that may function in neurotransmission. Experiments in this proposal examine the expression of neuroactive peptides by developing neural crest cells using radioimmunoassay and immunocytochemical techniques. The expression of selected neuroactive peptides will be examined in tissue cultures of neural crest cells and in neural crest-derived embryonic paravertebral sympathetic ganglia in vivo. This analysis will focus on which peptides are expressed, when this expression occurs, and possible factors that may influence the peptide content of these structures. These investigations may prove relevant to several neurocrist-opathic syndromes in which abnormal development of neural crest-derived cells occurs.